1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device for assuring a product based on the frequency of operation of the semiconductor device.
2. Background Art
Recently, semiconductor devices have been used for various applications such as consumer products and automobiles, the latter of which require high reliability, necessitating product assurances tailored for each application.
Conventionally, the assurance of the actual total operation time of a semiconductor device included in a product assurance is estimated based on the total time of use of a finished product, which in turn is estimated from the total number of uses and the frequency of use of the product, which are predicted for each application, and the maximum allowable number of uses of the semiconductor device.
However, the actual total operation time and the actual frequency of operation of a semiconductor device considerably vary depending on its use conditions and applications. As described above, the conventional method determines the total operation time of a semiconductor device only from the total time of use of the finished product. Therefore, if the semiconductor device is used such that its frequency of use is high, the performance of the semiconductor device deteriorates before a predetermined total time of use of the product elapses, which has caused a problem. If the semiconductor device is used such that its frequency of use is low, on the other hand, the semiconductor device is discarded after the predetermined total time of use of the product has elapsed even though the semiconductor device is still satisfying a desired performance. This means that a semiconductor device whose actual total operation time has not yet exceeded a predetermined allowable maximum value is wastefully discarded.
In view of the foregoing, the present invention has been made, and it is an object of the present invention to provide a technique for accurately detecting the actual total operation time of a semiconductor device based on its frequency of actual operation.
According to one aspect of the present invention, a semiconductor device comprises a nonvolatile memory, a volatile memory, and control means. The nonvolatile memory is for storing information on a frequency of operation. The information on the frequency of operation is rewritten in the volatile memory. The control means is for transferring the information on the frequency of operation stored in the nonvolatile memory to the volatile memory. The control means rewrites the information on the frequency of operation in the volatile memory. The control means returns the information on the frequency of operation to the nonvolatile memory.
By transferring information on a frequency of operation to a volatile memory, it is possible to rewrite the information on the frequency of operation in the volatile memory. Furthermore, by returning the rewritten information to the nonvolatile memory, the information on the frequency of operation can be held even after the power is turned off. With this arrangement, since it is possible to constantly check the frequency of use of the semiconductor device by reading out the storage contents of the nonvolatile memory, the user can use the semiconductor device while checking its frequency of use. The manufacturer, on the other hand, can design the semiconductor device so that the semiconductor device performs a predetermined operation according to its frequency of operation.
Other and further objects, features and advantages of the invention will appear more fully from the following description.